Is this doing assembly in the installer and getting window handles directly, then calling old school offsets into Win32 structs with DLL'd functions I don't see

Is this doing assembly in the installer and getting window handles directly, then calling old school offsets into Win32 structs with DLL'd functions I don't see the source to? Am I reading this right? It sets off my "malicious stuff" alarm but I'm not a security wonk. https://github.com/rain-1/filezilla-ng/blob/master/data/offer.nsh https://github.com/rain-1/filezilla-ng/blob/master/data/offe... We need to cut all that trash out.